In the rolling of metals such as aluminum and aluminum alloys, it is customary to flood the rolls and the workpiece with a coolant in order to carry away heat generated by the operation. It is also customary to use as a coolant an emulsion comprising water, mineral oil, and various additives having load bearing and friction-modifying properties to reduce friction between the rolls and workpiece. In order to perform satisfactorily in industry, the lubricant fluid must meet several important requirements.
Among the requirements for a satisfactory metalworking lubricant are stability under operating conditions and corrosion-inhibiting properties. In addition, the lubricant should not cause metal deposits on the rolls and workpiece during the rolling operation. Other important requirements include avoidance of excessive foam formation and thermodynamic characteristics to ensure wetting both the roll and workpiece.
Lubricant emulsions containing water and mineral oil are known in the prior art. While such emulsions may perform satisfactorily in achieving reduction of metal thickness, they are difficult to recycle for reuse. Removal of contaminants from used emulsion fluids requires separation of the oily and aqueous components. Such separation is expensive because it involves addition of chemicals to break the emulsion followed by storage of components in large settling tanks.
Garner et al U.S. Pat. No. 2,606,874 discloses a water-in-oil emulsion readily dispersible in water and consisting essentially of mineral oil, water, a water-soluble anionic surfactant and a 1,2-alkanediol "coupling agent" which is preferably 1,2-octanediol. An electrolyte (6 wt % sodium sulfate) is dissolved in the water in all four specific examples provided. The proportions of ingredients utilized by Garner et al are inconsistent with oil-in-water microemulsions.
Dreher et al U.S. Pat. No. 3,928,215 discloses cutting oil compositions that are said to be like liquid crystals. The compositions comprise a liquid hydrocarbon, water, an anionic surfactant and a cosurfactant which may be any of several different types of organic compounds. The cosurfactant is preferably an aliphatic alcohol and cyclohexanol is used in some examples. Dreher et al do not suggest using 1,2-alkanediols as cosurfactants.
It is a principal object of the present invention to provide a metalworking lubricant comprising an oil-in-water microemulsion that is thermodynamically stable under operating conditions and readily separable into oily and aqueous components for ease in decontamination and recycling.
It is a related object of the present invention to provide a lubricant having satisfactory metalworking performance characteristics.
Another object of the invention is to provide an environmentally acceptable lubricant. A preferred composition containing 1,2-alkanediol is much less toxic than prior art microemulsions containing short chain alcohols, which are extremely irritating.
Additional objectives and advantages of the invention will become apparent to persons skilled in the art upon reading the following detailed description of our invention.